1. Field of the Invention
The present invention relates to a method of making a rocker arm utilizable as an element of a valve mechanism in an automotive internal combustion engine.
2. Description of the Prior Art
Anti-wear rocker arms, as described in JP A Sho 63-303030, are producible as one piece from high chrome cast iron by casting. The anti-wear property results from high-hardness carbides such as (Fe, Cr).sub.7 C.sub.3 in the matrix.
High-hardness Fe-Cr-composite carbides tend to form a directional solidification in which acicular precipitates direct to the casting surface. When a rocker arm makes a sliding engagement with a cam member, the acicular carbides abrade the sliding surface of the associated cam member. It is known that acicular carbides can be rounded or globulized when tungsten is added in an amount of more than 10% by weight to the high chrome cast iron. However, it can not be a solution to the problem, because the addition of more than 10% of tungsten is costly. What is worse, tungsten produces tungsten carbides that are highly hard and abrasive to the cam member.